Many protesters wore masks, but crowds hindered social distancing measures for the large part.

Deputy Chief Medical Officer Paul Kelly on Sunday said community transmission was low, but warned there was the potential for asymptomatic carriers to spread the virus to others without realising it.

“This virus is very, very infectious,” the Australian Health Protection Principal Committee (AHPPC) said in a statement.

“Australians are reminded that in our recent past a single person infected more than 35 others.

“COVID-19 is transmitted via close contact, and large crowds and gatherings greatly increase the risk of infection, as the ability to maintain physical distancing is reduced.”

Authorities said it could take up to two weeks to determine whether the protests have caused a second outbreak of the virus.

At the moment, the World Health Organization (WHO) says it takes an average of five to six days for symptoms to arise.

But it could be a week or two before people realise they’re sick and go to be tested.

Depending on the patient, it could take health officials some time to trace cases back to the demonstrations.

Prof. Kelly said health officials could track the spread of the virus faster if all protesters downloaded the COVIDSafe tracing app.

“But realistically, mass gatherings of any reason including protests, at this time, are very risky, and I really would prefer it on medical grounds not to go ahead,” he said.

The protests took place despite Prime Minister Scott Morrison’s efforts to deter people from attending.

“I say to them, don’t go,” Morrison said on Friday.

Chief Medical Officer Brendan Murphy said the health advice was that mass public protests were too risky.

“A mass gathering, even if people try to make it safe by trying to practise distancing and hand hygiene, is inherently dangerous,” he warned.

“It would be very foolish to sacrifice … many of those gains by uncontrolled large gatherings.”

Victorian Premier Daniel Andrews urged people not to attend the Melbourne protest because it was “not safe”, but said police shutting down a demonstration would “inflame the situation”.

However, Victoria Police fined each of the protest organisers $1652 for breaching a public health order.